Slow tail compensation
View Patent ↗Systems and methods for slow tail compensation are provided. A photodetector signal is pre-amplified to thereby produce an uncompensated photodetector signal that includes a fast component and a slow component. The fast component is removed from the uncompensated photodetector signal to thereby produce a compensating signal that includes the slow component of the uncompensated photodetector signal. The compensating signal is subtracted from the uncompensated photodetector signal to thereby produce a compensated photodetector signal that includes the fast component but not the slow component.
1. A slow tail compensation system, comprising:
a preamplifier stage that amplifies a photodetector signal to thereby produce an uncompensated photodetector signal that includes a fast component and a slow component;
a slow tail compensator stage that removes the fast component from the uncompensated photodetector signal to thereby produce a compensating signal that includes the slow component of the uncompensated photodetector signal; and
a summing stage that subtracts the compensating signal from the uncompensated photodetector signal to thereby produce a compensated photodetector signal that includes the fast component but not the slow component.
2. The system of claim 1 , wherein the slow tail compensator stage includes:
a low pass filter that allows the slow component of the uncompensated photodetector signal to pass without allowing the fast component of the uncompensated photodetector signal to pass.
3. The system of claim 2 , where the slow tail compensator stage further includes:
an attenuator that causes the compensating signal, which is subtracted at the summing stage from the uncompensated photodetector signal, to have an amplitude corresponding to the slow component.
4. The system of claim 3 , wherein the uncompensated photodetector signal can be characterized by a fast time-constant (τ fast ), a slow time-constant (τ slow ), a fast amplitude contribution (A fast ) and a slow amplitude contribution (A slow ), and wherein a ratio of the attenuator is set to be substantially equal to the slow amplitude contribution (A slow ).
5. The system of claim 4 , wherein a time constant of the low-pass filter is set be substantially equal to the slow time-constant τ slow .
6. The system of claim 5 , further comprising:
a first register to store a value of the slow time-constant (τ slow ); and
a second register to store a value of the slow amplitude contribution (A slow ).
7. The system of claim 6 , wherein the values in the first and second registers can be changed using a controller.
8. The system of claim 5 , further comprising:
a first register bank to store a plurality of values for the slow time-constant (τ slow ); and
a second register bank to store a plurality of values for the slow amplitude contribution (A slow );
wherein a controller selects one of the values for the slow time-constant (τ slow ) stored in the first register bank and one of the values for the slow amplitude contribution (A slow ) stored in the second register bank.
9. The system of claim 1 , further comprising a photodetector that detects an indecent light signal and produces the photodetector signal therefrom.
10. The system of claim 1 , wherein the preamplifier stage includes a transimpedance amplifier.
11. The system of claim 1 , wherein the preamplifier stage includes a current-mode preamplifier.
12. The system of claim 1 , wherein the preamplifier stage includes a transimpedance amplifier and a voltage-to-current converter.
13. A method for slow tail compensation, comprising:
pre-amplifying a photodetector signal to thereby produce an uncompensated photodetector signal that includes a fast component and a slow component;
removing the fast component from the uncompensated photodetector signal to thereby produce a compensating signal that includes the slow component of the uncompensated photodetector signal; and
subtracting the compensating signal from the uncompensated photodetector signal to thereby produce a compensated photodetector signal that includes the fast component but not the slow component.
14. The method of claim 13 , wherein the removing step includes low pass filtering and attenuating.
15. The method of claim 14 , wherein the attenuating causes the compensating signal, which is subtracted from the uncompensated photodetector signal, to have an amplitude corresponding to the slow component.
16. The method of claim 13 , wherein the removing and subtracting are performed in the current domain.
17. The method of claim 13 , wherein the removing and subtracting are performed in the voltage domain.
18. A slow tail compensation system, comprising:
a means for pre-amplifying a photodetector signal to thereby produce an uncompensated photodetector signal that includes a fast component and a slow component;
a means for removing the fast component from the uncompensated photodetector signal to thereby produce a compensating signal that includes the slow component of the uncompensated photodetector signal; and
a means for subtracting the compensating signal from the uncompensated photodetector signal to thereby produce a compensated photodetector signal that includes the fast component but not the slow component.
19. The system of clam 19 , wherein the means for pre-amplifying includes one of a transimpedance amplifier and a current-mode preamplifier.
20. The system of claim 19 , wherein the means for removing includes a low pass filter.
21. The system of claim 20 , wherein the uncompensated photodetector signal can be characterized by a fast time-constant (τ fast ), a slow time-constant (τ slow ), a fast amplitude contribution (A fast ) and a slow amplitude contribution (A slow ), and wherein a time constant of the low-pass filter is set to be substantially equal to the slow time-constant τ slow .
22. The system of claim 21 , wherein the means for removing includes an attenuator, wherein a ratio of the attenuator is set to be substantially equal to the slow amplitude contribution (A slow ).